I don't think you could achieve that effect just with the hue saturation slider alone. Whichever colour you chose to reduce/increase, there would be some impact on the other colours which will all contain elements of it.
I'd say it's definitely been done by desaturating selected areas with individual masks, and would be pretty easy to do by using feathered masks which we've discussed several times.
It could also be done very easily by making a 1:1 copy toned in that blue grey tone overall and then just clone in the colored bits as required from the original.